A typical process in which this invention would be used would be the treatment of a silicon wafer to remove selected portions of a metal layer, exposing the silicon substrate. silicon substrates are known to be transmissive to light at certain wavelengths. Therefore, a light source may be directed toward the silicon wafer on one side and a detector positioned on the other side. The light transmitted through the wafer changes as the metal layer is removed and signals proportional to such changes are detected and utilized to determine such changes and to control the process, such as by signalling the endpoint of the process.
In prior art embodiments of apparatus to control etching and etching endpoints in wet etching systems a source optical assembly is mounted upon a moveable arm which extends into an etching chamber. The assembly must be movable so that it can be retracted during certain steps of the process, for example during the removal of the wafer from the etching chamber. Otherwise the bulkiness of the assembly causes it to intrude into the spray environment and interfere with the process. However, the moving of the assembly requires that it be repositioned when it is returned to the chamber and such removal and repositioning generally requires auxiliary motors and software for that purpose. For these reasons the use of such apparatus is not widespread.
This device is designed for incorporation in existing wet process semi-conductor etchers, (such as the 9100 series, manufactured by Applied Process Technologies) or for the replacement of prior art movable assemblies.